We intend to expand upon our preliminary data, and that of other investigators, which indicated that immunologic similarities exist between chemically-induced tumors. Cross-protection tumor challenge experiments and in vitro humoral cytotoxicity assays using 5 different syngeneic methylcholanthrene-induced sarcomas in inbred mice will be undertaken utilizing two modes of immunization: tumor growth and amputation, and multiple injections of irradiated cells. We will examine possible relationship between fetal and malignant cells by tumor challenge of animals immunized to fetal cells and by assaying the in vitro tumor cytotoxicity of fetal immune serum. The role of sexual differences in these immune responses will be studied. Also the effect of maternal sensitization to fetal antigens in utero on subsequent tumor challenge and cytotoxic antibody production will be examined. It is hoped that these studies will clarify the current hypothesis that, at least in part, neoantigens of malignant cells represent re- expressed fetal cell antigens normally present only transiently during fetal development, and that these fetal antigens are responsible for immunological similarity between chemically-induced experimental tumors.